After you've entered a couple of loading increments the software displays a graph of percent change, void ratio or deformation vs. log10(pressure) in the top-left portion of the screen. You can use this display to adjust the construction lines used to determine preconsolidation pressure (Pc) and the compression index (Cc), change the type of data used on the chart (percent change, void ratio or deformation, and D100 or final dial reading) and modify the chart's scales.
- If your curve appears upside down, you've probably made the wrong Dial values increase with compression check box selection.
- You can review the test data for any point on the compression curve by clicking on the point.
Selecting the Compression Curve Type
The Curve is box at the right of the compression curve box selects between plotting the compression curve as log10(pressure) vs. either void ratio, percent strain or deformation.
- The
Void ratioselection will be disabled if you haven't entered enough data to calculate void ratios.
Using D100 Values to Plot the Compression Curve
If you've taken time-rate data for some of your loading increments you can have the program use the deformation/void ratio/percent strain value calculated at D100 for these: increments as the point that the compression curve passes through instead of the result at the increments' final dial reading. (Doing so ignores the effects of secondary consolidation on the curve.) Loading increments without time-rate data (those for which a D100 value could not be calculated) would still be marked at the deformation/void ratio/percent strain value produced by their final dial reading.
- To use D100 values, click on the Use D100 values check box.
Construction Line Adjustment
The compression curve chart features two construction lines:
A blue line
This line is used to determine the compression index (Cc). It should be adjusted to be tangent to the steep, linear portion of the compression curve.
A vertical red line
This line is used to determine the Pc value. It should be adjusted left or rightwards until it intersects the point of maximum curvature on the compression curve.
- Please note that the intersection of the red line with the compression curve does not directly indicate the preconsolidation pressure. Rather, CONS uses this intersection as one of two parameters (along with the construction line tangent to the steep, linear curve portion) to Casagrande's graphical method of estimating preconsolidation pressure.
Both construction lines can be adjusted by dragging on their endpoints with the mouse while holding down the left mouse button. If you don't like the result, you can reset the construction line placement by clicking on the Reset Constructions button.
- As with the construction lines used to calculate time-rate Cv results, please treat the program's compression curve construction line placement as preliminary estimations. Each line's placement should be carefully reviewed before printing your final reports.